Spatial Variability of Soil Chemical Attributes Under Irrigation and No-Tillage System in Tropical Region.

Precision agriculture is a concept in soil, environment and crop management that involves knowledge of spatial and temporal variability of attributes within a field. The knowledge of the spatial variability of soil attributes and plants can help to identify the causes of variation in yield production. The objective of this work was to evaluate the spatial variability of soil chemical attributes in an area under irrigation and no tillage system. The experiment was conducted in São Carlos, São Paulo State, Brazil (21°57’15" S, 47°50’75" W, 850 m asl). The soil of the experimental area is a Typic Hapludox. The experimental area selected has two regions with variation in yield production. Soil geo-referenced samples were obtained at from the layers 0–0.1 m, 0.1–0.2 m and 0.2–0.3 m in a regular grid, spaced at 13 m intervals. Soil samples were prepared and submited to chemical analysis to evaluate the soil fertility. For each soil sample, pH, organic matter (OM), P, K⁺, Ca²⁺, Mg²⁺, Na⁺, S and H + Al content were determined. Descriptive statistical analyses (mean, median, maximum, minimum, coefficient of variation (CV), coefficient of skewness and coefficient of kurtosis) and geostatistics were calculated. The mean values of soil chemical attributes indicate that the identified region of high productivity showed higher values when compared with the region of low productivity. There was a decrease in the values of the chemical attributes throughout the soil profile, except for sulfate content, indicating leaching in subsurface layers. The variables studied showed high coefficient of variation in both regions, indicating a large variability.